The invention relates to an actuating mechanism for a clutch, and more particularly, an actuating mechanism for a clutch in which a control system receives target-value signals and an actual-value signal representing the actual clutch stroke, and which controls the clutch stroke according to the received target-value and actual-value signals by means of pressure transmitted to an actuating cylinder.
An actuating mechanism of this type is disclosed, for example, in EP-B-0 710 580. Such device enables an automatically regulated clutch actuation and an operator-dependent clutch actuation in a transmission for the purpose of shifting gears.
In the automatic clutch actuation, the control system regulates the stroke of the clutch via an electrically driven hydraulic master cylinder and a hydraulic slave cylinder integrated into the actuating cylinder upon receiving target-value signals and the actual-stroke signal. In accordance with the known device, the actual-stroke signal is obtained from a piston rod of the electrically driven master cylinder. The stroke of this piston rod has a fixed ratio to the clutch stroke. The actuating cylinder transmits the force exerted upon the slave cylinder piston by the pressure in the slave cylinder in the disengagement direction of the clutch, to the clutch. This force is, however, insufficient to actuate the clutch. For this reason, the pressure in the slave cylinder is also transmitted as control pressure to a proportional valve which allows pressure proportional to this control pressure to pass from a pressure source into the actuating cylinder, which thereby produces a sufficient force for the actuation of the clutch in its disengagement direction.
The operator-dependent clutch actuation is provided, in the known actuating mechanism, for purposes of permitting an emergency actuation of the clutch. The control system and the electrically driven master cylinder do not participate in this type of actuation. For this type of actuation, the operator produces the pressure in the slave cylinder integrated in the actuating cylinder which triggers the clutch via a master cylinder by means of an actuating element. This pressure is also transmitted to the proportional valve, which achieves the result described above. The force exerted in such instance by the slave cylinder piston can be designated as an operator force.
Due to the non-participation of the control system, the known actuating system offers only a non-regulated open loop operator-dependent clutch actuation. As a result, the sensitivity of the operator-dependent clutch actuation may be limited.
It is therefore an object of the present invention to improve the sensitivity of operator-dependent clutch actuation in an actuation system of the type mentioned above.